Physarum Polycephalum is a widespread eukaryotic microbe capable of producing effective networks between food particles to solve spatial planning problems. This paper investigates a previous algorithm for simulating Physarum Polycephalum. An open-source tool named Physarealm is developed for simulation in Rhino's graphical algorithm editor, Grasshopper. The tool adopts a previous stigmergic multi-agent algorithm for simulation and expands its boundary into three dimensions. In addition, this tool adds some custom rules, thus giving the designer more creative control over the produced results. Two research projects have applied this tool in the design process. The first project mainly takes advantage of the tool's path-planning ability, while the second one utilizes its aesthetic values, demonstrating the potential of the tool for further applications.